Measurement of free glucose turnover in brain.

A method has been developed for the measurement of the turnover rate constant or the half-life of the free glucose content of brain. It is based on an equation derived by the mathematical analysis of a kinetic model of the equilibration of the specific activity of the free glucose in brain with that of the plasma during an infusion of radioactive glucose. The method requires the measurement of the time course of the specific activity of glucose in the arterial plasma during an intravenous infusion of radioactive glucose for a period of 1 to 4 min and the specific activity of the free glucose in brain at the termination of the infusion. The turnover rate constant, or the half-life, is then calculated from these data by means of the operational equation of the method. The technique has been applied to conscious and anesthetized rats. In conscious rats the half-life of the free glucose content of brain was found to be 1.6 +/- 0.5 min (mean +/- S.D.) when the animals were killed by decapitation and 1.2 +/- 0.2 min (mean +/- S.D.) when they were killed by microwave irradiation; this difference is not statistically significant. In anesthetized rats, the half-life was found to be 2.6 +/- 0.8 min (mean +/- S.D.) in those killed by decapitation and 1.8 +/- 0.3 min (mean +/- S.D.) in those killed by microwave irradiation; this difference is statistically significant. The half-life of the glucose content of brain was found to be significantly prolonged during anesthesia and to be significantly and positively correlated with the plasma glucose concentration (r = 0.78; p < 0.001).